TRIBE OSTRACEA. 297 
arched at the other. Upper valve the smaller, flattish; its lamelle 
close-set, yellowish chocolate-coloured. Lower valve moderately 
hollowed, dirty purple; its distant lamelle arranged in rather nu- 
merous radiating ribs. Inside wholly white, except at the margin, 
which partakes of the external colouring. Denticles on one or both 
sides of the cartilage: inner edge elsewhere simple. 2. Adriatic; 
Black Sea. 
O. CocuiEaR. Poli, 2, t. 28, f. 28.—Lam. 5.—Phil. 1, p. 89. 
From oval to suborbicular, very thin, scarcely, if at all, lamellated, 
more or less tinged with rose-colour, glabrous; upper valve coneave 
externally ; lower valve deeper and larger, sometimes with more or 
less obsolete radiating ribs: inside whitish, its disk often stained 
with rufous-purple, edges simple, a few cardinal denticles near the 
apex ; scars placed nearer to the apex than to the rounded base. 24. 
Mediterranean. 
O. Cristata. orn, t. 7, f. 3—Poli, t. 28, f. 26, 7.—Phil. 1, 
p. 88; 2, p. 638.—O. C. var. C. Lam. 6. Ovate or orbicular, thin, ex- 
panded: upper valve much the smaller, shallow, white, beneath the 
concentric rows of dirty yellow imbricated flattened membranaceous 
lamelle ; lower valve rather profound, usually attached at the apex 
alone, whitish tinged with orange or pink, sometimes rayed with 
crimson lines, its lamelle strong, distant, curly, and moderately 
elevated, its folds arranged in radiating rows: inside silvery white, 
having distinct denticles near the incurved and pomted beaks ; scar 
moderate and reniform ; cartilage conical—Var. O. Depressa, Phil. 
1, p. 59, t. 6, f. 3. Attached by the entire surface ; concentric flakes 
few and distant; a few rosy rays. 3. Mediterranean. , The specimens 
of Lamarck’s Cristata in the Museum at Paris appear distinct, and 
of more than one species. The O. Exataiwa of Gmelin is founded on 
Knorr, 5, t. 14, f.4, which is apparently designed for a young example 
of this shell. 
O. Gatuina. Lam. 7.—Del. t. 18, f. 1. Obliquely ovate, small, 
rounded on one side, subreniform, whitish, glabrous: upper valve 
decidedly smaller, slightly convex: lamellae quite obsolete-—Var. 
Lower valve rayed with violet-coloured narrow ribs. Atlantic? The 
Jigure of Delessert much resembles (except in colouring) one of the many 
varieties of O. RatzopHore. It represents the interior as pure white, 
and exhibits no indications of ribs or lamell@ on either valve. 
O. Lineva. Lam. 9. ‘Thin, somewhat foliaceous, ovate-oblong, 
1 O, Numisma, Lam. 8, having been founded on a single wretched 
specimen in the Museum which is destitute of any decided charac- 
teristics, should be expunged from our catalogues. 
x 
